Magnetron



sept. 129 195o Filed Sept. l1, 1946 F. Lijm 2,522,184

MAGNETRON 2 S11eetsSheet l Eene/mice Ela) efe.

F. LUDl MAGNETRON sept. 12 195o 2 Sheets-Sheet 2 Filed Sept. 1l, 1946 Patented Sept. 12, 1950 MAGNETRON Fritz Ldi, Zurich, Switzerland, assigner to Patelhold Patentverwertungs- & Elektro- Holding A.G., Glarus, Switzerland Application September 11, 1946, Serial No. 696,117 In Switzerland September 15, 1945 2 Claims.

The present invention concerns a magnetron for generating ultra-short electromagnetic waves, an annular hollow body at least almost closed and bounded in a radial direction by two cylindrical casings being provided as the oscillation system, the cylindrical casing nearer to the axis being divided along the entire cylinder periphery into two parts by a tortuous slot. said two parts being at different alternating potential but at the same direct potential relative to the cathode located in the axis of the system.

The high frequency alternating field of the electron tube produces for instance by means of induction or inuence eiiect high. frequency currents in the tube parts, such as the cathode and the like, and. these currents cause a loss of high frequency energy. These losses can be ohmic or on the other hand they may be due to the radiation of high. frequency energy.

The present invention avoids these disadvantages land is characterised by the feature that at least a tube part which docs not belong to the tube oscillation circuit for determining the frequency and in which during operation high frequency currents occur, is connected to a lowradiation electrical oscillation system which is so tuned that the high frequency losses are at least approximately a minimum.

Several constructional examples of the inven tion are illustrated diagrammatically in Figs. 1-5 of the accompanying drawing.

Fig. l shows a tube according to the invention in cross-section, and Fig. 2 a constructional form of an oscillation system for reducing the losses and connected to the heating circuit system, Whilst Fig. 3 shows the combination of a loss-reducing oscillation system with a permanent magnet. Fig. Il illustrates a modiiied form of the invention where the oscillation system is used simultaneously for extracting the high frequency energy. Figs. c and 5b show two tube sections at right angles to each other.

In Fig. l the cross-scction is taken Ialong a plane passing through the tube axis. Reference numeral l indicates the electron-emitting hot cathode which in this case is in the form of a spiral, 2 is an annular cavity resonator of rec tangular cross-section at anode potential, 3 `are the leads for the heating current, and 4 is an energy extracting vor collecting electrode. The capacitive part of the cavity resonator is mainly formed by the segments 5 arranged next to each other in the circumferential direction. The tube is loc-ated inside a glass vessel 25. The method of operation of the tube is already described in my copending application Serial No. tl7,533, filed March 5, 1943, and does not therefore need to be repeated again.

The leads for the heating current are constructed Lecher lines which are closed by a capacity E. The Lecher line can be varied for instance by shifting the capacity l5 together with its leads 'l along the Lecher system 3. The oscillation system comprising the Lecher system 3, capacity ii together with the leads l, and the cathode l, is according to the invention tuned in such a manner that the high frequency losses are a minimum. Tuning is not only possible by altering the electrically effective length of the Lecher line. The capacitance of condenser 6 can also be varied.

The heating current for the cathode l is supplied over the side plates ll which serve to support the former. Ii the side plates and cathode are electrically separated from each other, it is ad- 'vis-able to tune both by means of special oscillation systems so as to reduce the high frequency losses to a minimum. Tuning for minimum high. `frequency losses is generally `achieved when the length of the Lecher line amounts to an uneven multiple of a quarter wave length of the prevailing oscillations, preferably equal to M4.

Generally it is an advantage when the high frequency oscillation circuits are mutually decoupled. It is advisable to decouple the oscillation circuits in order to reduce the high frequency losses and also to decouple these circuits from for instance the energy collecting electrode Afl. With Lecher lines such decoupling can be achieved by arranging the Lecher lines perpendicular to each other.

In the constructional form according to Fig. 2 where only the cathode l and the leads 3 are shown, in order to prevent undesirable radiation at one end of the conductor, a screening pot i6 in the form of a concentric Lecher line short-circuited at one end is arranged in place of a tuned two-Wire Lecher line. Screening pot I6 has a length of l/fl or an uneven multiple of same, )l being the Wave length of the electromagnetic oscillations of the magnetron tube. They screening not can be located inside or outside the tubevessel.

Fig. 3 shows a constructional form of the tube without glass vessel. Reference numeral l' again indicates the cathode, 2 the cavity resonator, and 3, 6 the low-radiation tuneable oscillation system, Whilst 4 is the energy collecting electrode and 5 the anode segments; I1 are the poles of a magnet.

Since the cathode is surrounded by the magnetic lines of force of the high frequency oscillations of the cavity resonator, these induce electric currents in the cathode which due to the tuning of the heating conductors are prevented from flowing away over the heating current source. Appreciable Wattless currents therefore flow in the oscillation circuit which blocks the high frequency. With the constructional form according to Fig. 4 these currents are used for collecting the high frequency energy. In this ligure there is a cavity resonator 2 Iand a cathode l With current leads 3. Tuning is achieved by means of impedance I8; an element which has capacitive and/ or inductive properties. With this form of the invention there is also a low-loss conductor connected in parallel with the heating spiral l, so that the high frequency oscillation system is as far as possible free from losses. To prevent the heating current from flowing through this conductor, one end of this latter is connected over a capacitance 20 to the oscillation circuit for reducing the high frequency losses, so that there is a separation of the direct current kind. Electrode 2l serves to collect the high frequency energy.

In Fig. 5a the plane on which the cross-section is taken lies in the axis of the tube, whilst Fig. 5b is a sectional View along a plane perpendicular to the tube axis. The same elements as in the previous figures are indicated by the same reference numerals. 26 is a getter device. System 23, 24 is again tuned in such a manner that the high frequency losses are a minimum, and the Lecher line 22 together with the variable capacitance 21 serves to tune the natural frequency. Both oscillation systems shown in Figs. 5a and 5b are merely diagrammatic. Loop 2l serves for collecting the high frequency energy and passing it on to the consumer.

As a result of coupling the cavity resonator oscillations with the currents flowing in the oscillation circuits, the frequency of the oscillations of the cavity resonator can be influenced by varying the tuning of the oscillation circuits. It is therefore advisable to make the impedance I8 variable. In a modified form of the invention the impedance i8 consists of a cavity resonator.

Another modified constructional form of the invention is obtained by substituting a tube arrangement, which acts as a variable condenser, for the capacitance 6 of Fig. 1, this tube being influenced for instance by altering the grid bias. This enables the tube oscillations to be modulated.

Iclaim:

l. A magnetron for generating ultra-short electromagnetic waves comprising, within an evacuated envelope, a hollow cavity resonator having inner and outer cylindrical Walls connected by end walls, the inner cylindrical wall being divided into a plurality of parallel anode segments connected in alternation to the respective end walls, means for establishing a magnetic field within the cylindrical space defined by said anode segments and parallel to the axis thereof, a cathode extending through said cylindrical space and having an axis substantially parallel to the axis thereof, side plates arranged perpendicular to the axis of and spaced axially from the respective end walls of said cavity resonator, said cathode being electrically connected to and supported by said side plates, leads electrically connected to the respective side plates and extending to the exterior of said envelope, and a condenser connecting said leads and cooperating therewith to form a Lecher line non-resonant at the frequency of the generated oscillations.

2. A magnetron as recited in claim 1, wherein said envelope is of metal and constituted in part by the outer cylindrical wall of said cavity resonator.

FRITZ LDI.

REFERENCES CITED The following references are of record in the le of this patent:

UNTIED STATES PATENTS Number Name Date 2,128,235 Dallenbach Aug. 30, 1938 2,149,024 Lindenblad Feb. 28, 1939 2,157,179 Linder May 9, 1939 2,163,589 Dallenbach et al. June 28, 1939 2,167,201 Dallenbach July 25, 1939 2,207,846 Wolff July 1G, 1940 2,421,636 McArthur et al. June 3, 1947 2,432,571 Haeif Dec. 16, 1947 

